Mild air oxidation of boron nitride nanotubes. Application as nanofillers for thermally conductive polycarbonate nanocomposites

Boron nitride nanotubes (BNNTs) have experienced considerable growth in recent years due to their unique intrinsic properties, in particular for the fabrication of polymer nanocomposites. Dispersion of pure BNNTs in nanocomposites is often difficult due to their poor compatibility with most polymer matrices. An approach involving the creation of hydroxyl groups on their surface could improve their dispersion. While some harsh oxidation processes have been reported so far, a mild oxidation of BNNTs using air as the oxidant is reported here. This new catalytic reaction leads to slightly oxidized BNNTs, which were characterized by scanning electron microscope, x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis. Polycarbonate nanocomposites were then fabricated using pristine and oxidized BNNTs as nanofillers. The measured thermal conductivity increased linearly with the mildly oxidized BNNTs content. It reached a five-fold increase up to 1.19 W m.K-1 at 15% vol. content which is significantly improved over nanocomposites fabricated with severely oxidized BNNTs, while the electrically insulating character remained unchanged.